Wednesday, January 21, 2009
The fields have always attracted a lot of birds -- I wrote about the numbers seen on this year's Christmas Bird Count. The very first winter the original field hosted an unusual bird: a European Goldfinch (Carduelis carduelis), a bird not native to North America. European Goldfinches are common in the pet trade, and it's not too unusual to hear about sightings of escaped or released pets. Unlike members of the parrot family, European Goldfinches are very hardy and can survive northern winters. The sighting occurred during a time when I had been hearing more and more reports of European Goldfinch sightings, especially in the Chicago area. Curious, I posted a page on the RRBO web site requesting sightings from the upper Midwest (a current version of the page is here). I also kept my eyes on the various Internet birding lists and regional publications.
That there were a lot of European Goldfinches out there readily became apparent. I compiled over 400 reports, of which 298 were from Illinois, Wisconsin, Indiana, and Michigan. There was a clear concentration in southern Wisconsin and northern Illinois, a pattern of radiation from the "epicenter" that was more pronounced north than south, and a smattering of reports over the rest of the four states.
It is believed that the bulk of these European Goldfinches -- as well as a handful of other European cage bird species that were reported in the same areas -- originated with a bird importer in the greater Chicago area. From a number of independent reports I received, this importer had apparently deliberately released these species on more than one occasion over time. Believe it or not, as long as the birds are legally imported, there is no federal law prohibiting their release, even if they are not native.
Since 2003, there have been reports of nesting European Goldfinches in northern Illinois. They may also be nesting in southern Wisconsin. Great Tits (Parus major), another one of the species involved in the alleged releases, have also nested in southern Wisconsin and northern Illinois! European Goldfinches nest earlier in the year than American Goldfinches and appear to be ecologically benign, although non-native species frequently end up having unanticipated impacts on ecosystems. Whether the breeding population will grow and persist is not known. In the early part of the 20th century, there were a couple of established colonies in New York, founded by deliberate releases. They eventually died out. However, the proliferation of non-native plant species -- many of which are the natural foods of European Goldfinch -- may prove to be a boon for the species this time around.
I don't believe the majority of the Michigan sightings (or the many Ontario reports I've gotten) of European Goldfinches are attributable to same source. The geographic and chronological patterns do not seem to fit. Some are likely just escaped pets. Many others may be deliberately released birds. Some pockets of reports came from areas with higher populations of people that practice eastern religions, which sometimes advocate setting birds free to accrue merit in the afterlife. Employees at my own local pet store, which often carry European Goldfinches for sale, reported to me that these and other cage birds are sometimes purchased by people of various ethnic backgrounds with the intention of releasing them. I presume this is the source of the Dearborn European Goldfinch.
I ended up writing a detailed account of the reports I received, including background on the ecology and history of European Goldfinches in the U.S. and additional information on their future, in a paper that was just published in North American Birds; you can click on the link to download a PDF copy:
Craves, J. A. 2008. Current status of European Goldfinch (Carduelis carduelis) in the western Great Lakes region. North American Birds 62:2-5.
UPDATE, JUNE 2009: I have posted an update regarding nesting European Goldfinch in Illinois.
Photo of European Goldfinch in France by Daniel (ParaScubaSailor) at Flickr under a Creative Commons license.
Friday, January 16, 2009
Consider this fact: Up to 90% of the insects that feed on plants can only reproduce on the plants with which they share an evolutionary history. Plants and insects are engaged in a long, evolutionary arms race. Plants develop special compounds to ward off the insects that eat their leaves. Since plants are unable to flee, these specialized defenses are their primary protection against herbivory. In response, insects develop adaptations that allow them to tolerate or overcome the toxins produced by plants. Plants, then, must respond with new chemicals which in order to be effective must be increasingly unique to particular plant families. As a result, many plants have a relatively small suite of insects that are able to eat them (and consequently, reproduce on them).
This is a very slow process. A plant transported to a new place in which it has no close relatives is generally without enemies. Native insects are unable to quickly adapt to a stranger’s chemical defenses. This is one reason why many non-native plants become invasive; there is little to keep them in check. More importantly to our discussion is the fact that even well-behaved, non-invasive ornamental plants typically lack or have few insect pests.
And therein lies the problem for birds. Not only are many bird species dependent on insects all year, 96% of all North American land birds raise their young on insects, all or in part. A lack of insects, especially in the breeding season, results in fewer young birds being raised, and eventually population declines.
Tallamy is a co-author of a fantastic new paper in the scientific journal Conservation Biology* The paper describes a study which examined just how many fewer insects were available to birds on non-native plants. Six pairs of suburban sites in Pennsylvania were compared. They were similar in size; total plant cover; number of plant species; presence of bird boxes, feeders, or baths; and surrounding characteristics. The only difference between paired sites was that one was landscaped entirely with native plants, while the other was a more typical suburban mix of native canopy and non-native groundcovers and shrubs. The results were profound:
- Native sites had four times more caterpillars (an extremely important source of food for birds, and the main source of food for most nestlings)
- Native sites had three times more caterpillar species
- Birds were 54% more abundant in native sites
- There were 66% more bird species in native sites
- There were 77% more pairs of breeding birds in native sites (117% more native bird species on native sites)
"We provide evidence that the landscaping choices of homeowners affect populations of both birds and the insect food they require, thus empowering homeowners, landscapers, and policy makers to raise (or lower) local carrying capacities by plant choice alone."Individuals can make a difference. The choice is yours. Choose natives!
Download RRBO's "Landscaping for Migratory Birds" (PDF) for suggestions on native plants and useful links.
Top photo: Eight-spotted Forester (Alpia octomaculata) on Virginia Creeper (Parthenocissus quinquefolia). Photo by Julie Craves. Bottom: Brown-hooded Owlet (Cucullia convexipennis) on goldenrod (Solidago sp.). Photo by Darrin O'Brien.
*Impact of native plants on bird and butterfly diversity in suburban landscapes. 2009. Burghardt, K. T., D. W. Tallamy, and W. G. Shriver. Conservation Biology 23:219-224.
Tuesday, January 6, 2009
One of the annual challenges is counting the hoards of birds that hang out at the nine or so sunflower/wildflower fields planted by Ford Motor Company around Dearborn. After trying several strategies, we now devote a single team (usually Darrin and I) to spend most of the day concentrating on getting accurate counts of birds in the fields. This helps prevent double-counting if the birds move from field to field, and allows a team to spend the necessary time to make good estimates on what are sometimes very sizable flocks of sparrows or finches.
This year was made a bit easier, as the largest field, on the south side of Hubbard at Southfield, was not planted this year. Another, at Southfield and Rotunda, was plowed under in fall. Still, we had our work cut out for us. The photo below is the field on the north side of Hubbard at Southfield. I've underlined myself in red! This field had the most birds this year. It took us a long time, but we feel comfortable with our count of over 2400 House Sparrows here. These fields have a lot of benefit to wildlife, but the downside is that they have certainly helped boost the House Sparrow population, which has skyrocketed in the last few years. Our final total of nearly 3500 House Sparrows set a new high record.
Another group of birds that has begun to overwinter in these fields are blackbirds. Last year the Rotunda and Southfield fields had a staggering 1300 Brown-headed Cowbirds. This year the blackbird flock was more modest. Here's about half of them. Most were Red-winged Blackbirds, along with some cowbirds and a single Common Grackle. Raptors have taken advantage of all the small birds in these fields, and once again we have a wintering Merlin here. We had plenty of opportunities to watch it hunt!
If we have time in the afternoon after going through the sunflower fields, Darrin and I hit a few other spots. We had this female American Kestrel dining on a mouse near Miller Road and Wyoming.
It's always nice to have a hot cup of coffee when adding up the numbers back at the EIC on campus. Here I am with Jerry Sadowski (in the Crocs that match the rest of his outfit!), Greg Norwood (in ball cap), and Gary Hutman, all veterans of the Dearborn count. Jerry and Greg are in charge of counting on campus, and Gary covers Rouge Park (in Detroit, but within the larger count circle).
The final story is the continuing saga of the lack of crows since West Nile Virus wiped them out in this area. Up to 2003, it wasn't unusual to count well over 200. That year, we counted 18. Since then, we haven't had more than 8 in any year. Blue Jay numbers, however, have remained pretty constant.
You can view the results of all past Dearborn CBCs on the RRBO web page.